and longitude form a grid that measures distance from a reference point. You will learn
about this type of grid when we discuss maps later in this chapter.
Direction
If you are at a laptop, you can change your location. When an object is moving, it is not
enough to describe its location; we also need to know direction. Direction is important for
describing moving objects. For example, a wind blows a storm over your school. Where is
that storm coming from? Where is it going? The most common way to describe direction
in relation to the Earth’s surface is by using acompass. The compass is a device with a
floating needle that is a small magnet (Figure2.1). The needle aligns itself with the Earth’s
magnetic field, so that the compass needle points to magnetic north. Once you find north,
you can then describe any other direction, such as east, south, west, etc., on acompass
rose(Figure2.2).
Figure 2.1: A compass is a device that is used to determine direction. The needle points to
the Earth’s magnetic north pole. ( 41 )
A compass needle aligns to the Earth’s magnetic North Pole, not the Earth’s geographic
North Pole or true north. The geographic North Pole is the top of the imaginary axis upon
which the Earth’s rotates, much like the spindle of a spinning top. The magnetic North Pole
shifts in location over time. Depending on where you live, you can correct for this difference
when you use a map and a compass (Figure2.3).
When you study maps later, you will see that certain types of maps have a double compass
rose to make the corrections between magnetic north and true north. An example of this
type is a nautical chart that sailors and boaters use to chart their positions at sea or offshore
(Figure2.4).